The present invention relates to a dry etching process and to an etching apparatus and more particularly relates to techniques for controlling etchant gas feed and control of the reactor flow during a dry etching process.
Plasma-type etching processes using, for example, tetrafluoromethane (CF.sub.4) gas, have come to be widely used in place of solution-type etching in the production of semiconductor devices. Plasma-type etching utilizes a reactive gas in a radio frequency glow discharge to etch silicon and its compounds, such as silicon nitride and silicon oxide, and also molybdenum layers and tungsten layers. Plasma-type etching and reactive ion etching have sometimes been referred to as dry etching or dry process technology. The basic aim in dry process technology is to provide most favorable conditions of etching rate, uniformity of etching, selectivity and etch definition. Prior art dry etching processes were sometimes defective in that an uneven distribution of positive and negative ions in a high electric and magnetic field lead to irregular etching.
The general flow characteristics of the etchant gas in dry process technology, due to the high vacuum used in this technology, are in the domain of rarefied gas dynamics. Specifically, the gas flow occurs in the ranges of free-molecular flow and the transition flow regime which occurs between free-molecular flow and continuum flow. Thus, the flow behavior in the reactivity zone is characterized by predominately molecular collision phenomena. Continuum fluid mechanics are not useful to predict mass flow effects under the reactor conditions encountered in dry processing techniques.
In general, the present state of dry processing technology is such that etching performance variation occur under various operating conditions. The principal variation which affects etching performance is the character and uniformity of the gas field in the reactivity zone surrounding the etching object. The present invention is directed to new techniques and apparatus for generating and controlling uniform, highly effective gas field characteristics in a reactivity zone.